Forests, through growth of trees and an increase in soil carbon, contain a large part of the carbon stored
on land. Forests present a significant global carbon stock. Global forest vegetation stores 283 Gt of
carbon in its biomass, 38 Gt in dead wood and 317 Gt in soils (top 30 cm) and litter. The total carbon
content of forest ecosystems has been estimated at 638 Gt for 2005, which is more than the amount of carbon
in the entire atmosphere. This standing carbon is combined with a gross terrestrial uptake of carbon, which
was estimated at 2.4 Gt a year, a good deal of which is sequestration by forests. Approximately half of the
total carbon in forest ecosystems is found in forest biomass and dead wood.

Other terrestrial systems also play an important role. Most of the carbon stocks of croplands and
grasslands are found in the below-ground plant organic matter and soil.

Human activities, through land use, land-use change and forestry (LULUCF) activities, affect changes in
carbon stocks between the carbon pools of the terrestrial ecosystem and between the terrestrial ecosystem
and the atmosphere.

Management and/or conversion of land uses (e.g. forests, croplands and grazing lands) affects sources and
sinks of CO2, CH4 and N2O. According to the IPCC WGIII (2007), during the decade of the 1990s,
deforestation in the tropics and forest re-growth in temperate and boreal zones remained the major factors
contributing to emissions and removals of greenhouse gases (GHG) respectively. The IPCC WG1 (2007) reported
that estimated CO2 emissions associated with land-use change, averaged over the 1990s, were 0.5 to 2.7 GtC
yr–1, with a central estimate of 1.6 GtCyr-1.

The role of LULUCF activities in the mitigation of climate change has long been recognized. Mitigation
achieved through activities in the LULUCF sector, either by increasing the removals of GHGs from the
atmosphere or by reducing emissions by sources, can be relatively cost-effective.

General mitigation options could include forest-related activities such as reducing emissions from
deforestation and degradation, enhancing the sequestration rate in new or existing forests, and using wood
fuels and wood products as substitutes for fossil fuels and more energy-intensive materials. A variety of
options for mitigation of GHG emissions also exists in other land systems. The most prominent example is
agriculture, where options include improved crop and grazing land management (e.g., improved agronomic
practices, nutrient use, tillage and residue management), restoration of organic soils that are drained for
crop production, and restoration of degraded lands.

However, the main drawback of LULUCF activities is their potential reversibility and non-permanence of
carbon stocks as a result of human activities, (with the release of GHG into the atmosphere), disturbances
(e.g. forest fires or disease), or environmental change, including climate change.